INVESTIGADORES
FERNANDEZ Diana Elizabeth
congresos y reuniones científicas
Título:
Xiphosurid trackways in a marginal marine setting from the Lower Cretaceous (Agrio Formation) of the Neuquén Basin, Argentina.
Autor/es:
FERNÁNDEZ, DIANA E.; PAZOS, PABLO J.
Lugar:
Sao Leopoldo
Reunión:
Congreso; Iº Latin American Symposium on Ichnology; 2010
Institución organizadora:
UNISINOS
Resumen:
The Agua de la Mula Member of the Agrio Formation (Late Hauterivian-EarlyBarremian)
is a mixed carbonate-siliciclastic, mainly marine and marginal-marine
succession, exposed in the Neuquén province, Argentina. The bed
containing the trackways (K level) corresponds to one of the uppermost
levels of this unit, approximately 8 m below the contact with the
Huitrín Formation, in the outcrops located at Cerro Rayoso. It is part
of a 7.5-m-thick interval that begins with siltstones with poorly
preserved desiccation cracks, followed by a thin heterolithic interval
with organic debris, limestones having desiccation cracks, and a
sandstone bed with abundant Rhizocorallium. This interval is followed by
a sandstone (K level) containing very well-preserved ripples. These
have mostly sinuous crests, but in some parts they tend to be
unconnected, forming linguoid ripples. Some are flat-topped ripples,
reflecting subaerial exposure. The dominant eastward paleocurrent
reflects an onshore flow direction. The xiphosurid trackways are
preserved as negative epireliefs, recording surface impressions and
shallow undertracks . They are assigned to Kouphichnium Nopsca 1923. The
trackways are highly abundant and display a number of preservational
variations depending mostly on their orientation with respect to the
ripple crests and undertrack fallout. They are mostly preserved on the
crests and are parallel to them. In some cases, they climb up and down
the ripple crests and troughs. Telson impressions are conspicuous and
continuous but not always present. Regular leg and "pusher" leg marks
are common. Another ichnotaxa found in the K level are Gordia,
Cochlichnus and ?Treptichnus; they were produced after the xiphosurid
trackways and under a thin water film. These xiphosurid trackways
represent the first known evidence of the existence of these traces in
the Cretaceous of the Neuquén Basin.